Composites of reinforcements and thermosetting matrix materials can be formed by various molding techniques such as pultrusion, filament winding, vacuum molding, compression or injection molding and open lay-up molding. The resulting composites can be used in such applications as automobile components, boat hulls and fishing rods.
The configuration and type of reinforcement have a pronounced effect on the physical characteristics of the composite, such as density, compressive strength and shear strength. Preferred reinforcement configurations often vary greatly for different molding processes and molding conditions.
The matrix material selected can also influence the selection of reinforcement type and configuration. For example, reinforcements typically used for reinforcing thermoplastic matrix materials may not be compatible with thermosetting molding operations. In thermosetting molding operations, good "wet-through" (penetration of the polymeric matrix material through the mat) and "wet-out" (penetration of the polymeric matrix material through the individual bundles or strands of fibers in the mat) properties are desirable. In contrast, good dispersion properties are of predominant concern in typical thermoplastic molding operations.
For reinforcing plastic articles, U.S. Pat. No. 3,614,936 discloses a nonwoven structure of chopped glass strand which is stitched together. Optionally, the nonwoven structure can include parallel glass strands lengthwise of the structure (see col. 6, lines 48-55). The stitched nonwoven structure can be compacted with heated rollers to fuse the stitching thread and then needled (see col. 4, lines 14-30).
U.S. Pat. No. 4,749,613 discloses a thermoplastic stampable sheet composed of 30 to 80 percent by weight of reinforcing fibers arranged in one direction needled together with a swirled continuous strand mat, the sheet being impregnated with a thermoplastic resin.
U.S. Pat. No. 4,931,358 discloses a material consisting of a thermoplastic polymer and a needled textile fabric consisting of at least two layers of continuous filament yarn oriented in at least one preferred direction and at least one layer of unoriented fibers.
U.S. Pat. Nos. 5,540,986 and 5,129,131 disclose a stampable sheet of thermoplastic resin reinforced with a glass fiber mat having a layer of non-oriented fibers and a layer of unidirectional fibers which are mechanically intertwined.
None of the foregoing references address the problems encountered in molding thermosetting composites, such as wet-out and compatibility between the reinforcement and the thermosetting matrix material.
U.S. Pat. No. 4,278,720 discloses a mat useful in thermosetting sheet molding compounding which has two layers of parallel strand oriented at a 45 degree angle to the longitudinal axis of the mat and a layer of randomly oriented strand positioned therebetween, the points of intersection of the strands being bonded by an organic binder, as discussed at column 2, lines 26-35. Use of organic binders in mat formation is not desirable for environmental reasons.
There is a long-felt need in the thermosetting molding industry to provide a glass fiber reinforcement which is compatible with thermosetting matrix materials, which can be used in a wide variety of thermosetting molding applications to provide good uniformity and handling characteristics and which provides a composite having good physical properties such as flexibility, strength and high density.